CA1100458A

CA1100458A - Centrifugal water oil separator

Info

Publication number: CA1100458A
Application number: CA328,606A
Authority: CA
Inventors: John K. Sammons; Charles H. Fox, Jr.
Original assignee: Continental Oil Co
Current assignee: ConocoPhillips Co
Priority date: 1978-08-28
Filing date: 1979-05-29
Publication date: 1981-05-05
Also published as: EP0008393A1; US4175040A; JPS5531500A; DE2962808D1; EP0008393B1; DK273379A; NO792176L

Abstract

CENTRIFUGAL WATER OIL SEPARATOR
Abstract of the Disclosure A centrifugal oil-water separator comprising an inner spinning bowl having openings near the lower outer periphery for passage of water therefrom into an outer bowl which remains stationary. The oil-water mixture is passed to the upper center of the spinning bowl with separation of the oil and water therein, concentrating the oil near the top of the inner bowl and disposable water is removed from the outer bowl.

Description

CENTRIFUGAL WATER OIL SEPARATOR
This in~ention relates to a method Eor recover ing oil intermixed with water. More particu]arly, this invention relates to a method for recovering oil intermixed with water by use of a centrifugal separator which is sim~
ple in nature and requires ~o chemical separating agents.
S~vere environmental problems have occurred from water pollution caused by accidental spills or leak-age of petroleum or o-ther hydrocarbon liquids into bodies of water. These spilled materials are dang~rous to marine life, wildlife living on or near the water, and have made rivers and oceans asthetically unpleasant. Many methods have been devised for combating such accidental spills.
For example, some devices involve skimming the body o~ water to remove an upper oily layer employing blades, bel~s, absorbant rollers and the like. These methods suffer from several disadvantages among which are intricate machinery, low rates of recovery, and inability to operate effectively where wave action is high. These recovery devices usually are moved about on the water surface to contact the oil film in order to a~fect recovery, or have been employed with additional devices to bxing the oily film to the recovery apparatus.
Many devices have been shown in the prior art for such recoveries. Amony these are U~S. Patent 4 t 038,182 which discloses an oil-water s parator for removing films of oils from the surface of water, wherein the oily film and water flows into a vortex formed by an impellar section and then outwardly into a housing wherein oil in a layer o enhanced thickness is collected and drawn off from time to time. U~S. Patent 3,800,951 discloses a separator for removing films of oil from the surface of water wherein a vortex is formed by an impeller within a housing just below the surface of the water. -The oil constantly collects in the vortex and is drawn off by various means. Examination of the figures of these two references will show them to be complex and designed for moving about in bodies of water.
U.S. Patent 3,311,296 discloses a centrifugal separator which separates mixtures of brine, hyd~ocarbons . . .
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; ' , ' ' ~2--and solidified wax using a spinning bowl. While the reference is directed toward -the separation of solids from liquids, the brine and hydrocarbon liquid would be inher-ently separated in such an apparatus. However, an exami-nation of the apparatus itself shows it to be clumsy, intricately constructed and subject to many malfunctions in commercial use.
U.S. Patents 1,839,941 and U.S. 1,018,878 both show a slurry of solids and liquid which is put into the lower end of frustroconical spinning tubular bowl with liquids and fines passing through openings therein into a trough collector while large solids pass over the top into a second trough collector. Other references :illus-trative of this art are U.S. Patents 4,044,626; 2,~80,873;

2,831,369; 2,711,827; 2,534,194; and 1,782,224.
However/ these references are designed to remove films from the surface of water, which object is usually frustrated by wave action, and/or are so constructed as to require -the use of separating agents and sophisticated mechanical equipment.
However, hydrocarbon water mixtures may be liquid (or on occasion solids in the divided state) which are less dense than the liquid on which it is spread. In many cases there is no clear-cut film of water on the top for the apparatus to separate. In the specification which follows, the terms "water" and "hydrocarbon" or "oil" will signify respectively the body of liquid and the substance intermixed with said liquid, but it will be clear that the use of these terms is not intended to be o~ a restrictive nature.
Water used in production methods is also subject to being contaminated with hydrocarbons. This water, before being returned to the environment, must normally meet con-centration levels sufficiently low to allow the environment to degrade the mixed hydrocarbons without harm. The xe-covered oil is processed as production oil.
~lowever, in times of high production or in times of equipment failure, the water exiting these clean up ..

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-3 devices is often intermixed with hydrocarbons a-t a sufficiently high level to preventreturn of said water to the environment.
For example, on offshore production platforms~ low pressure separators such as corregated plate interceptors are used to separate oil from water. In the.se interceptors, which are essen-tially settling tan]cs having large surface area plates therein to allow oil and water time to separate, allowiny the oil to be skimmed from the surface and the water returned to the environ-ment~ it has often been found th.at as high as 1,000 parts per million oil concentration remains in the water. United States government limits for water returning to oceans is 50 parts per million, and many states have lower limits near the coastline, such as ~ouisiana with 3Q parts per million. Similar environ-mental limits exist or are contemplated throughout the world.
It would therefore be of great benefit to provide a simple, efficient apparatus for reducing the oil conten-t o water recovered from production means and withdrawn from contaminated areas to levels environmentally acceptable. It is therefore an object of the present invention to provide an apparatus and method for removing oil from water. Other objects will become apparent to those skilled in this art as the description proceeds.
In the drawings, Figure 1 shows a partial cutaway top view of an apparatus embodying the present invention; Figure 2 dis-closes generally a side sectional view of Figure 1 along section 2-2 thereof; Figure 3 discloses an alternate liquid leveling means replacing the weir plate disclosed in Figures 1 and 2 and Figure 4 shows a perspective view of the liquid leveling means.
The invention consists .in an apparatus for recovering oil from oil water mixtures comprising two nested bowls; an outer stationary and an inner rotating bowl having an annulus there~
between, the inner bowl having a flange affixed to the upper periphery thereof and covering a portion of the bowl interior, each howl being penetrated by a shaft, said shaft being rigidly affixed to tha inner bowl and rotatably attached to the outer bowl by means sealing the shaft aperature from liquid passage, said shaft connected at the lo~er. end to motive means capable of rapidly rota~ing said shaft and at the upper end to a perfor-'' '. '. ;. '' :~.

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-3a-ated basket rigidly fixed to said shaft, said inner bowl having multiple aperatures in the lower portion thereof and multiple aperatures at the upper periphery thereof substantially adjacent said flanye and a groove or channel in the annulus rigidly affixed to said stationary outer bo~l at a level ~elow the level of the upper aperatures in the rotatable inner bowl, the lower portion of said channel in fluid communlcation with the exterior of the stationary outer bowl and at least one aperature in the lower portion of the outer bowl in fluid communication with a fluid leveling means capable of balancing inflow and outflow.
The invention also consists in a method for continuously recovering oil from oil-water mixtures comprising placing a stream of oil-water mixture into an oil-water separator having an outer stationary bowl and an inner rotatable bowl having an annwlus therebetween, the inner bowl having a flange affixed to the wpper periphery thereof and covering a portion of the bowl interior, each bowl penetrated by a shaft said shaft being rigidly fixed to the inner bowl and rotatably attached to the outer bowl by means sealing the shaft aperature from liquid passage, said shaft having at the upper end a dispersant means rigidly affixed to said shaft, said inner bowl having multiple aperatures in the lower portion thereof and multiple aperatures at the upper periphery thereof substantially adjacent said flange, and a groove or channel in the annulus between the bowls, ri~idly fixed to said stationary outer bowl at a level below the level of the upper aperatures in the periphery of the rotatable inner ~owl, said channel being in fluid communication with the exterior of the outer bowl; at least one aperature in the lower portion of the outer bowl in fluid communication with a fluid leveling means capable of ~alancing inflow and outflow, wherein oil-water mixture entering the rapidly rotating dispersing means passes into the rapidly rotating inner bowl, separates into heavier water in the lo~er portion thereof and lighter oil at the upper portion thereof, the centrifugal force passing the oil : 35 to the upper portion thereof and through said aperatures into a channeI from wh.ich oil is recoYered, and water is passed through the lo~er aperatures thereof into the annulus from whence said ~ater flows to a fluid leveling means whereby the inflow and outflow are balanced.

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-3b-The method according to the instant invention comprises the steps of centrifugally separating the oil and water using an inner spinning bowl having openin~s near the lower outer periphery for passage of wat:er therefrom into an outer bowl which remains stationary. The oil-water mixture is inserted into the upper center of the inner spinning bowl with separation of the oil and water therein and concentration of the oil near the top of the inner bowl. Disposable water is removed from the outer bowl and oil is recovered from a trough adjacent the top of the spinning inner bowl.
The invention is simple, has no complicated internal structure, and has a minimum of moving parts for easy maintenance. The inner bowl is rotated at a speed effective to make oil climb to the exit ports in the upper rim thereof.
The speed of the inner bowl's rotation is not fixed, depending as \it does upon the diameter of the bowl . . . . . . . . . . .

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and the concentration of oll in water. However, -the re-volutions per minute (rmp) of the spinning inner bowl will normally be from about 75 to about 90 rmp based upon a 24 inch diameter inner bowl. Such an apparatus can, of course, be constructed at any desired size, but normally in com-mercial applications would be of a size capable of handling from about 1,000 to 2,000 barrels per day of oil-water mixtures. An apparatus having an inner bowl of three feet diameter and three feet in depth should separate about 1,000 barrels per day of oil-contaminated water.
The invention is more concretely described and can be more clearly explained with reference to the drawings.
Generally described, the drawings show a top and side view of a centrifugal oil-water separator having an inner spinning tub or bowl, said bowl having openings near the lower outer periphery for passage of water therefrom into an outer bowl which remains stationary and openings near the upper outer periphery of the inner bowl for passage o oil therefrom into a channel rigidly affixed to the sta-tionary bowl in the annulus between the nested bowls. The oil-water mixture is inserted in the upper center of the rapidly rotating inner bowl with consequent separation of the oil from the water therein and concentration of the oil near the top of the rotatable inner bowl and passage of substantially oil free water from the inner bowl to the outer bowl.
Specifically des~ribed, Figure 1 shows a partial cutaway top view of an apparatus of the instant invention.
In the figure the apparatus used comprises an outer bowl (1) having affixed to the upper periphery thereof a flange (2) extending -toward the inner bowl (3) which in turn has a flange (4) extending toward the interior of the inner bowl.
The outer bowl is stationary and is supported by convenient supports (5) which can be of any physical configuration sufficient to support the weight. The bowls are penetrated by a shaft (6) which is rigidly fixed to a perforated basket (7) having aperatures (8) therein. The oil-water mixture to be separated enters the apparatus through an inlet conduit (9) which passes the mlxture to be separated directly into ,,, the perforated basket. The oil-water mixture is rotated at a speed sufficient to .~orce the oil ~10) to the surface of the water, said oil being concentrated near multiple aperatures (11) substantially adjacent the Elange at the outer periphery of the inner rotating bowl, said aperatures being in direct commun,icatlon to the channel (12) which i~s rigidly affixed to the outer bowl (1) at a distance below the upper aperatures (11) of the rotating inner bowl (3)O
Optionally, pipes or conduits (.13) can be affixed to these upper aperatures in order to facilitate passage of the recovered oil to the channel (12~, which is in fluid com~
munication with the exterior o~ the stationary bowl (14), The apparatus also describes an overflow weir (15~ having an adjustable means (16) to level the amount o~ water leaving the apparatus in relation to the oil-water mixture entering the apparatus.
Figure 2 generally describes a side sectional view o~ Figure 1 along section 2-2. In addition to the com~
ponents already described, it is apparent that the inner and outer nested bowls are penetrated completely b~ a sha~t (6 which is connected to a motive means (17~ through drive means (18) capable o~ xapidly rotating the inner bowlO The shaft penetrates the outer bowl through a seal;ng means (19) capable of preventing ~luid passage therethrough while allowin~ the shaft to rapidly rotate. The inner bowl is penetrated at its lower portion by multiple aperatures ~20~
which allow the passage o~ substantially oil free water (21) to the outer bowl, said water then passing into the liquid leveling means (22) which is attached to the overflow weir and adjusting means and is connected to the outer bowl through an aperature ~23). The inner bowl optionally con-tains small flanges (30) verticall~ attached io the inner wall to lmpart motion to the bowl contents. therein. The figure also describes an optional trap (24) for solid con-taminant , having an aperature therein ~or removal o~ said settled contaminants from time to time. The separated oil (10~ exits the channel (12) through an aperatuxe (14) while the recovered, substantiall,y oil ree water exits the level-ing apparatus through an overflow weir (lS).

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~ 5a -F.iyure 3 describes an alternate liquid leveling means to replace the weir plate described in Figures 1 and 2.
The liquid level is adjusted by simply raising or lowexing the hose such that the overflow occurs at: the liquid level desired in the rotating drum. Figure 4 i.s a perspective v c; the liquid leveling means.

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In practice then, the method of the instant in-vention comprises placing an oil-water mixture (25) into a dispersing apparatus (7) which is at the center of a rapidly rotating bowl or tub 13). Oil free water is normall~ addèd to the apparatus prior to beginning insertion of the oil-water mixture in order to prevent premature escape of oil through the lower aperatures (20) of t.he inner bowl (3) prior to the apparatus having operational capacity of an oil-water mixture. Once the inner bowl is rapidly rotating ~ :
and the oil-water mixture is inserted into the dispersing means (7) 7 the centrifugal force of the rapidly ro~ating inner bowl tends to force the lighter oil to the upward outer periphery of the bo~l and through the multiple aper-atures at the upper periphery of the inner bowl into the channel rigidly affixed ~o the stationary outer bowl. The channel is provided with an oil drain to remove the re-covered oil. The inner bowl and, optionally the outer bowlr are fitted with flanges projecting toward the interior of the respective bowls in order to prevent escape`of oil due to the centrifugal force of the separating means,althouqh when in proper balance the outer bowl flange is not neces-sary. Water recovered from the oil-water mixture exits the inner bowl through the aperatures at the lower portion of the bowl and enters the annulus between the twa nested bowls. The water level is critical to the method of the instant invention and must be carefully adjusted by the use of an overflow weir or other leveling means. The amount of recovered oil and substantiall~ oil free water removed from the apparatus must equal the inflow of oil~water mixture to be separated for the method to operate efficiently. This is most easily accomplished by simply adjusting the amount of water leaving the over~low weir.
In addition, the~figure shows an optional con~
taminant trap useful when.the oil-water mixture contains large amounts of sediment and sand.
Thus the apparatus and method described provi~des a si.mple method for separating oil from water mixtures with a minimum of moving parts and simple eonstruction details. It will be clear to those skilled in the art that instructio : 40 details can be varied somewhat from the descri~tion shownO

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For example, the outer bowl could be a square, rectangular, or other geometric configuration so long as the channel is circular and collects the oil which exits the inner rotating bowl through the ports around the upper periphery. The water level-ing means shown in Figure 3 is by a simple hose adjusted atvarying heights to control the water level in the inner bowl and -the annulus between the inner and outer bowl. Means for removing solid contaminants entirely around the lower periphery of the ou-ter bowl could likewise be provided ~or example.
A model apparatus was built having an inner drum diameter of about 24 inches. A mixture of oil and water from a low pressure separator containing various amounts of hydro-carbons was inserted into the apparatus. The inner drum was rotated at approximately 80 rpm. Samples were collected as the oil-water mixture entered the separator and samples of exit water were collected to determine the levels of hydrocarbon therein. The test was carried out and samples collected at times of 1/2 hour, 1 hour, and 1 1/2 hour duration. At 11:00 a.m. the inlet boil concentration was 52 parts per million from the low pressure separatorl unacceptably high for transmittal to the environment. The outlet water contained 10 parts per million oil. At 11:30 a.m. the inlet water contained 44 parts per million oil, while the water outlet concentration dropped to 7 parts per million oil. At 12:30 p.m. the inlet oil con-centration was 2~ parts per million and the outlet waterconcentration was 3.5 parts per million. At 2:00 p.m. the inlet oil concentration had risen to 50 parts per million and the outlet water concentration was at a low 12 parts per million.
~ second oil mixture was passed through the oil-water separator. The mixture was carefully designed to contain about 40~ oil by weight. The mixture was passed into the separator for a time sufficient for an equilibrium to be reached.
Analysis of the exit water showed only 17 parts per million oil in the water exiting the separator.
It can be seen from the actual examples carried out that essentially complete separation of oil-water mixture is obtained. The oil does not have to be dispersed upon the ~ . . : .
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surface o~ -the mixture entering the separator, although such a dispersal would be separated as easily as intermixed oil-water mixture.
As set forth above, the instant invention re~uires no chemical aids for separation, thus insuring the purity of the water removed and the non-contamination of the oil recovered.
Normally the oil content of the water entering the apparatus will range from abou~ 2S parts per million to about 50~ by weight. ~Iowever, the apparatus is entirely capable of separating even higher oil contents and effi-ciently yielding purified water. Normally the oil in the water outlet will range from about 3 parts per million to about 50 parts per million depending upon the method of operation and the proper balancing of the separated oil. If greater purity is desired several such apparatus could be utilized in seriest the exit water from the first passing through the second and so on. Such a series would effect-ively remove oil from the water in a simple efficient and rapid manner. Normal oil concentrations in water exiting the apparatus from a first pass basis would range in the area of about 12 parts per million based on normal water concentration inputs of about 50 to about l,000 parts per million, using water from conventional separating methods which is unacceptably high in oil content. Water cleansed of hydrocarbons by the method of the instant invention is sufficiently pure to be returned to the environment.
While certain embodiments and details have been shown for the purpose of illustrating this invention, it will be apparent to those skilled in this art that various changes and modifications may be made herein without departing from the spirit or scope of the invention.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for recovering oil from oil water mixtures comprising two nested bowls; an outer stationary and an inner rotating bowl having an annulus therebetween, the inner bowl having a flange affixed to the upper peri-phery thereof and covering a portion of the bowl interior, each bowl being penetrated by a shaft, said shaft being rigidly affixed to the inner bowl and rotatably attached to the outer bowl by means sealing the shaft aperature from liquid passage, said shaft connected at the lower end to motive means capable of rapidly rotating said shaft and at the upper end to a perforated basket rigidly fixed to said shaft, said inner bowl having multiple aperatures in the lower portion thereof and multiple aperatures at the upper periphery thereof substantially adjacent said flange and a groove or channel in the annulus rigidly affixed to said stationary outer bowl at a level below the level of the upper aperatures in the rotatable inner bowl, the lower portion of said channel in fluid communication with the exterior of the stationary outer bowl and at least one aperature in the lower portion of the outer bowl in fluid communication with a fluid leveling means capable of balancing inflow and outflow.

2. An apparatus as described in Claim 1 wherein the upper aperatures of the inner bowl are attached to hose or pipe means of sufficient length to transport fluid to said channel.

3. An apparatus as described in Claim 1 wherein the outer bowl has a flange affixed to the upper periphery.

4. An apparatus as described in Claim 2 wherein the liquid leveling means is an adjustable weir plate.

5. An apparatus as described in Claim 2 wherein the liquid leveling means is a hose.

6. An apparatus as described in Claim 4 wherein the lower portion of the outer bowl has means for removing settled solid contaminants.

7. A method for continuously recovering oil from oil-water mixtures comprising placing a stream of oil-water mixture into an oil-water separator having an outer sta-tionary bowl and an inner rotatable bowl having an annulus therebetween, the inner bowl having a flange affixed to the upper periphery thereof and covering a portion of the bowl interior, each bowl penetrated by a shaft said shaft being rigidly fixed to the inner bowl and rotatably attached to the outer bowl by means sealing the shaft aperature from liquid passage, said shaft having at the upper end a dis-persant means rigidly affixed to said shaft, said inner bowl having multiple aperatures in the lower portion thereof and multiple aperatures at the upper periphery thereof sub-stantially adjacent said flange, and a groove or channel in the annulus between the bowls, rigidly fixed to said stationary outer bowl at a level below the level of the upper aperatures in the periphery of the rotatable inner bowl, said channel being in fluid communication with the exterior of the outer bowl; at least one aperature in the lower portion of the outer bowl in fluid communication with a fluid leveling means capable of balancing inflow and outflow, wherein oil-water mixture entering the rapidly rotating dispersing means passes into the rapidly rotating inner bowl, separates into heavier water in the lower por-tion thereof and lighter oil at the upper portion thereof, the centrifugal force passing the oil to the upper portion thereof and through said aperatures into a channel from which oil is recovered, and water is passed through the lower aperatures thereof into the annulus from whence said water flows to a fluid leveling means whereby the inflow and outflow are balanced.

8. A method as described in Claim 7 wherein solid contaminants are removed from the bottom of the oil water separator.

9. A method as described in Claim 7 wherein the ratio of oil to water is from about 25 parts per million to about 50 percent by weight.